Recovery of trichlorobenzene



2,725,408 RECOVERY OF TRICHLOROBENZENE Lucy Merritt, Oak Park, Mich., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application July 31, 1952, Serial No. 301,983

2 Claims. (Cl. 260650) The present invention relates to the recovery of trichlorobenzenes, particularly from trichlorobenzenes that have been sulfonated.

Sulfonated trichlorobenzene appears to be particularly reluctant to desulfonate under the standard desulfonating treatments, such as steam distillation or boiling with 85% sulfuric acid in water.

Among the objects of the present invention is the avoidance of the above difiiculty.

Further objects of the present invention include the provision of a desulfonating technique for readily hydrolyzing sulfonated trichlorobenzenes back to trichlorobenzene.

The above as well as still further objects of the present invention will be more clearly understood from the fol-- lowing description of several of its exemplifications.

According to the present invention, the desired desulfonation is readily eifected by heating the sulfonated trichlorobenzene with an aqueous sulfuric acid having an acid concentration of 75 to 90 per cent by weight, while bubbling an inert gas through the hot mixture to flush out vapors of desulfonated trichlorobenzene. Advantageously this is followed by cooling the effluent gas to thereby cause the trichlorobenzene vapor which is carried off in this gas to be condensed from it.

A feature of the invention is that the desulfonating acid can be the same reagent producing the original sulfonated trichlorobenzene, but with additional water added to bring down the acid concentration towithin the effective range.

Although it is not clearly understood just how the desulfonation of the present invention takes place, it has been observed that when the passage of the inert gas is interrupted, the desulfonation is markedly reduced in velocity and apparently completely stops after it progresses to a small extent, regardless of the acid strength used.

As illustrative of the present invention, a mixture of sulfonated trichlorobenzenes was first prepared by sulfonating a commercial mixture of chlorobenzenes derived from the dehydrochlorination of insecticidal inactive benzene hexachloride isomers. The dehydrochlorinated mixture contained:

68.4% of 1,2,4-trichlorobenzene 24.7% of 1,2,3-trichlorobenzene 1.0% of 1,2-dichlorobenzene 1.5% of 1,3-dichlorobenzene .6% of 1,4-dichlorobenzene 1.8% of 1,2,4,S-tetrachlorobenzene .7% of 1,2,3,4-tetrachlorobenzene .6% of l,2,3,S-tetrachlorobenzene the remainder being essentially pentachlorocyclohexene. The sulfonation was carried out in a four-necked flask 2,725,408 Patented Nov. 29, 1955 ICC? equipped with stirrer, thermometer, dropping funnel and reflux condenser. The latter was connected to a drying tube to keep out moisture present in the atmosphere. Sulfuric acid in an amount equal to the weight of the mixed chloro compounds, was utilized as the solvent. The mixed chloro compounds were added to the acid and the mixture stirred and heated until a temperature of C. was reached. Suflicient 15 per cent fuming sulfuric acid was added to react with all the l,2,3-trichloro-' benzene present. When the addition was complete, heating and stirring was continued for 4- /2 hours. The reaction mixture was allowed to cool and separated into two layers. The top layer, which consisted of unsulfonated chloro compounds was removed. As a result of this treatment, the 1,2,3-trichlor0benzene was essentially completely sulfonated, while the 1,2,4-isomer was largely unreacted. Thus a means of separation of the two isomers was provided. The lower layer, which was the acid layer, was diluted with water until an acid content of 85 per cent was reached.

The diluted layer was then reheated without transferring it from the original reaction container and nitrogen was bubbled through by means of an additional tube inserted into the flask. At the same time, the reflux condenser was replaced by a conventional distillation condenser. A slow stream of nitrogen, barely sufficient to make itself felt, caused trichlorobenzene and water to distill over at a relatively high rate and a 56 per cent yield of desulfonated trichlorobenzene was thus recovered.

The same reaction-promoting effect of the nitrogen stream is obtained when a sulfonated pure 1,2,4-trichlorobenzene, pure 1,2,3-trichlorobenzene, or pure 1,3,5-trichlorobenzene is used in place of the above mixture. Combinations of these trichlorobenzenes also respond in 'the same manner.

In place of nitrogen other inert gases such as helium, or other noble gases, carbon dioxide, carbon monoxide, oxygen, or air can be used with equal effectiveness. Water vapor does not appear to be inert for the purposes of the desulfonation reaction which involves hydrolysis.

As many apparently widely diiferent embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof except as defined in the appended claims.

I claim:

1. The method of treating a mixture of 1,2,3- and 1,2,4- trichlorobenzenes which comprises the steps of heating the mixture with an anhydrous sulfuric acid to partially and disproportionately sulfonate the trichlorobenzenes, then removing the unsulfonated trichlorobenzenes which are now richer in the 1,2,4-isomer, diluting the remainder of the reaction mixture with water to a sulfuric acid concentration of from 75 to 90 per cent by weight, heating the thus diluted material and bubbling an inert gas through it to carry off vapors of desulfonated trichlorobenzenes and cooling the efiluent gas to condense out these trichlorobenzenes.

2. The method of claim 1 in which the inert gas is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF TREATING A MIXTURE OF 1,2,30AND 1,2,4TRICHLOROBENZENES WHICH COMPRISES THE STEPS OF HEATING THE MIXTURE WITH AN ANHYDROUS SULFURIC ACID TO PARTIALLY AND DISPROPORTIONATELY SULFONATE THE TRICHLOROBENZENES, THEN REMOVING THE UNSULFONATED TRICHLOROBENZENES WHICH ARE NOW RICHER IN THE 1,2,4-ISOMER, DILUTING THE REMAINDER OF THE REACTION MIXTURE WITH WATER TO A SULFURIC ACID CONCENTRATION OF FROM 75 TO 90 PER CENT BY WEIGHT, HEATING THE THUS DILUTED MATERIAL AND BUBBLING AN INERT GAS THROUGH IT TO CARRY OFF VAPORS OF DESULFONATED TRICHLOROBENZENES AND COOLING THE EFFLUENT GAS TO CONDENSE OUT THESE TRICHLOROBENZENES. 